The pyrogenic exotoxins of Group A streptococci and the enterotoxins of Staphylococcus aureus, which are also pyrogenic exotoxins, constitute a family of structurally related toxins which share similar biological activities (11, 13). The staphylococcal and streptococcal pyrogenic exotoxins also share significant amino acid homology throughout their sequences (11, 19, 40). This pyrogenic exotoxin family contains nine main toxin types, and several allelic variants (subtypes) have been described. Several studies have shown that the toxins share common motifs based on immunologic cross reactivity between the toxins (26, 27). These toxins share the ability to bind the major histocompatibility complex (MHC) molecules of infected hosts, as well as the variable beta chain of the T-cell receptor complex (TCR), causing an aberrant proliferation of specific T-cell subsets (3, 4, 12). This property of the toxins has labeled them as "superantigens" (36) since they do not interact with the MHC and TCR molecules in the manner of conventional antigens (14, 18).
These bacterial toxins cause a variety of syndromes in humans. Staphylococcal enterotoxins have been implicated in staphylococcal food poisoning (26), as well as toxic shock like syndromes (1). The gene sequences and deduced amino acid sequences of at least six staphylococcal enterotoxins ("SE"): A, B, C, D, E and H, are known, i.e., SEA, SEB, SEC, SED, SEE, and SEH (19, 23). The streptococcal pyrogenic exotoxins ("SPE") have been implicated in causing the symptoms of scarlet fever and toxic shock like syndrome (8, 20, 30). The sequences of three members of this family are known: SPEA, SPEC, and SSA (5, 23, 35).
Toxic shock syndrome toxin (TSST-1) from S. aureus shares similar biological activity with the enterotoxins and streptococcal pyrogenic exotoxins, however it is not as closely related structurally (2). Toxic shock syndrome can be exacerbated by the synergistic effects of TSST-1 with the enterotoxin/pyrogenic toxin family of toxins (9, 25). Gram negative bacterial endotoxin and the pyrogenic toxins can work synergistically to produce lethal toxic shock (17, 30).
"Toxic shock like syndrome" is the term previously used to describe the syndromes caused by staphyloccal and streptococcal pyrogenic bacterial exotoxins other than toxic shock syndrome toxin (TSST-1) from S. aureus. Currently, the term "toxic shock syndrome" is used to describe the syndromes caused by TSST-1 and the other pyrogenic exotoxins, and is the terminology used hereinafter.